Electronic shelf labels are beginning replacing paper shelf labels in supermarkets. For each product placed on a shelf, a modern electronic label can display both information for consumers (price, unit price, promotion . . . ) and information for employees of the store (inventory, facing, barcode . . . ).
Generally, electronic labels are wirelessly connected to a main server located somewhere in the store, in which data about all products is managed. This server is traditionally connected to the store back-office, in order to be gather all information required to display on the ESL. Several radio technologies are commonly used, including WiFi, radio waves or infrared transmission.
The information displayed by the labels is regularly updated. Prices may evolve, configuration of shelves may change. To this end, protocols of transmission are used to send messages from the server to the targeted labels.
Existing protocols generally meet all the expectations for supermarkets and hypermarkets in which the electronic shelf labels use Segmented Display technology. However when graphic display technology, i.e. a 2-dimensional array of lit or unlit pixels (also named “DotMatrix Display” technology) is used, existing protocols require some advanced compression techniques to meet customer expectations in terms of throughput and ESL update rate.
Nowadays, groups of stores pool their supplying process by using central purchasing back-offices. These entities enable to leverage the purchasing power of the stores to obtain discounts. Several hundreds of stores may depend of the same central purchasing back-office, and therefore share the same products.
In such a case, it should be interesting to manage data about these products not store by store, but in a centralized way at the central purchasing back-office level. But as the number of electronic labels commonly reach tens of thousands in hypermarkets, managing simultaneously hundreds of stores (i.e. millions of labels) becomes problematic in terms of processing time. At this scale, the amount of data to be treated at each update may indeed overpass computation capability of the most powerful servers. Gaps of several minutes may then appear between the launching of an update by the server and the effective display update of the labels, which could mislead customers and generate errors, if shifts occur between displayed prices and real prices.
These problems will still increase in coming years, as new labels are expected, these labels being provided with large high-resolution LCD screens, or even with color displays.
Moreover, it should be interesting to manage not only the electronic labels, but other media displaying devices which are often found in large stores, like plasma screens, for displaying special offers, advertising, etc.
A first solution to this problem is to directly send raw data to the media displaying devices. These data are less voluminous, but have to be processed by the device itself for being displayed. It requires complex devices comprising an improved treatment unit, and possibly a memory. These media displaying devices are more expensive, and above all consume more energy, which is not acceptable in particular for electronic labels which only comprise an embedded small battery whose lifetime is long but limited.
International patent application WO03/073261 proposes a method for lowering the energy consumption when updating the display with new product information. The idea is to update only the part of the display which has to be updated. Messages are sent in coded text, and displays are derived from this text and from fonts stored in each label.
However, if this method reduces the problem, it does not solve it. Indeed, the needed computation power remains proportional to the number of labels in the different stores connected to the central purchasing back-office. Besides, labels require enough memory for storing every font of the store in every size.